The present invention relates to apparatus and methods for extruding coating onto a conductor. More particularly, the present invention relates to an extrusion tool for extruding a coating jacket onto at least one pre-coated conductor.
In the manufacture of multi-conductor cables, it is necessary to provide an extrusion apparatus capable of applying a coating jacket to a bundle of wires wherein individual wires in the bundle may already have been covered with a layer of insulative coating. In cases where a single type of coating jacket material is used, extrusion tools have been designed to apply the jacket material as a single layer to the pre-coated wire bundle. However, processing speeds are limited with such tooling arrangements.
Co-extrusion processes (i.e., processes involving the simultaneous application of multiple layers of coating material to a conductor) provide better processing speeds but have heretofore been used where two or more types of coating material are to be applied from separate material reservoirs. See, for example, U.S. Pat. No. 4,303,734 to Sullivan; U.S. Pat. No. 1,859,901 to Trebes.
Moreover, existing co-extrusion processes suffer from numerous problems which render them unattractive for use where only a single type of coating material is to be applied. For example, control of coating material temperature is more difficult where a co-extrusion process is used because the coating material to be used in the various layers is typically drawn from separate reservoirs.
In addition, it is often the case that outgassing occurs when multiple coating layers are applied to a wire or the like, resulting in formation of bubbles (and resultant cavities) between the layers. The bubble formation can cause separation or peeling of the layers. To address this problem, many co-extrusion devices are augmented with a source of vacuum to evacuate gas bubbles from the area between the layers as the layers are deposited. The use of a vacuum source significantly increases the processing time and can result in waste of the coating material.
Existing processes also generally require the use of filler materials to fill voids between the conductor bundle and the coating jacket. Some existing tooling is designed specifically to allow paper tape filler to be wrapped around the conductor. See, for example, U.S. Pat. No. 4,568,507 to Baxter. Breakage of the paper tape, resulting in excessive downtime, is a common problem with tooling which relies upon paper tape filler.
Other multiple layer extrusion process, and tooling used therein, is designed to place various types of filaments between the conductor and the jacket to serve both as filler and as reinforcing material. For example, U.S. Pat. No. 4,132,756 to Ferrentino et al. relates to a process for extruding plastomeric or elastomeric material onto at least two filaments.
According to the present invention, an extrusion tool is provided for extruding a coating jacket onto at least one pre-coated conductor. The extrusion tool comprises a frame, a first conical element mountable in the frame, a second conical element mateable with the first conical element, and a die mountable in the frame. The frame is formed to include a port positioned to receive the coating. The first conical element is formed to include a bore, the bore being sized to allow passage of the pre-coated conductor (or conductor bundle) therethrough.
The second conical element cooperates with the first conical element to define a first flow passageway therebetween. The first flow passageway is positioned to receive the pre-coated conductor as it exits from the bore and is connected in fluid communication with the port to supply an initial portion of the coating jacket from the port to the pre-coated conductor as the pre-coated conductor exits the bore and enters the first flow passageway. In addition, the second conical element also includes a tapered portion. The second conical element terminates in a cylindrical tip.
The die cooperates with the tapered portion and the cylindrical tip of the second conical element to define a second flow passageway therebetween. The second flow passageway is in fluid communication with the port to supply a final portion of the coating jacket from the port to the pre-coated conductor as the pre-coated conductor exits the first flow passageway.
Advantageously, the tool provides for separation of the coating jacket material into the first and second flow passageways and remarriage of the material as initial and final portions of the coating jacket in such a manner that no gassing occurs, eliminating the need to provide a vacuum source.
Further advantageously, the initial portion of the coating jacket is applied to the at least one pre-coated conductor so as to create an inwardly-projecting rib extending between the initial portion of the coating jacket and the pre-coated conductor. The rib fills voids between the jacket and the conductor, eliminating the need for paper filler. The rib also provides reinforcement, eliminating the need to provide filaments around the conductor.
The present invention also relates to a method for extruding coating from a single source onto at least one pre-coated conductor. The method involves use of an extrusion tool including a frame, the frame being formed to include an interior region including a cylindrical portion and a port for communicating coating from the single source to the interior region. The extrusion tool further includes means for providing a branched flow passageway in the interior region, the providing means terminating in a cylindrical tip mateable with the cylindrical portion so that the branches of the branched flow passageway are concentric at their downstream ends.
The method comprises the steps of arranging the providing means in the frame so that approximately 65% or less of the cylindrical tip extends into the cylindrical portion, moving the conductor into the interior region, feeding the coating from the single source to the port, flowing a first portion of the coating from the port through a first branch of the branched passageway for extrusion onto the conductor as an initial portion of the coating jacket, and flowing a second portion of the coating from the port through a second branch of the branched passageway for extrusion onto the conductor as a final portion of the coating jacket.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.